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Abstract:

An eyeglass (10) is adapted for providing an ophthalmic vision and a
supplementary vision to a wearer of said eye-glass, both ophthalmic and
supplementary visions being sharp during respective periods. To this
purpose, a transparent active device (3) is located between the back face
(BF) of the eyeglass and a light-conducting element (2), this latter
being embedded within the eyeglass and dedicated to output the light of
the supplementary vision. The transparent active device switches between
two optical power values, which are dedicated to make sharp the
ophthalmic vision and the supplementary vision, respectively.

Claims:

1. An eyeglass for providing at least an ophthalmic vision and a
supplementary vision to a wearer of said eyeglass, and comprising: a
front face and a back face, intended to be oriented respectively away
from and towards an eye of the wearer; a light-refracting transparent
material comprised between the front face and the back face; a
light-conducting element located in the light-refracting transparent
material, and adapted to output a supplementary light between the front
face and the back face of the eyeglass, through an exit face of said
light-conducting element and towards the wearer's eye, the ophthalmic
vision corresponding to a natural image formed by light transmitted by
the eyeglass from the front face to the back face thereof, and the
supplementary vision corresponding to a supplementary image to be viewed
by the wearer and formed by the supplementary light, the light-conducting
element being further transparent for the light of the ophthalmic vision;
and a transparent active device located between the exit face of the
light-conducting element and a portion at least of the back face of the
eyeglass, said transparent active device being configured to produce a
variable optical power depending on a control signal supplied to said
transparent active device, with first and second values for said variable
optical power which are different from each other and correspond
respectively to a first and a second state of the transparent active
device, said transparent active device in the first state being effective
for the supplementary light, and the first value of the variable optical
power being suitable for the supplementary image to appear sharp to the
wearer, and said transparent active device in the second state being
effective for the light of the ophthalmic vision transmitted through the
exit face of the light-conducting element, and the second value of the
variable optical power being suitable for the natural image to appear
sharp to the wearer.

2. An eyeglass according to claim 1, wherein the transparent active
device is entirely embedded within a rear portion of the light-refracting
transparent material located between the exit face of the
light-conducting element and the back face of said eyeglass.

3. An eyeglass according to claim 1, wherein the transparent active
device is liquid crystal-based.

4. An eyeglass according to claim 3, wherein the transparent active
device comprises a portion of liquid crystal contained between two
surfaces, at least one of said surfaces being provided with a Fresnel
pattern, and further comprises two electrodes arranged for modifying an
orientation of said liquid crystal upon a variation of an electrical
voltage applied to said electrodes.

5. An eyeglass according to claim 3, wherein the transparent active
device comprises an array of cells juxtaposed parallel to the exit face
of the light-conducting element, and separated from each other by a
network of walls each extending perpendicular to said exit face, each
cell containing a portion of liquid crystal, and the transparent active
device further comprises at least two electrodes arranged for modifying
an orientation of the liquid crystal portion in each cell upon a
variation of at least one electrical voltage applied to said electrodes,
the respective liquid crystal portions of the cells being suitable for
the transparent active device to produce the variable optical power.

6. An eyeglass according to claim 1, wherein the difference between the
first and the second values of the variable optical power of the
transparent active device is not equal to an optical power of the front
face of the eyeglass.

7. An eyeglass according to claim 1, wherein the difference of the first
value minus the second value for the variable optical power of the
transparent active device is greater than an optical power of the front
face of the eyeglass, in signed values.

8. An eyeglass according to claim 1, wherein the second state is a
default state of the transparent active device.

9. An eyeglass according to claim 1, wherein respective areas of the
transparent active device and the exit face of the light-conducting
element match each other when projected along light rays of the
ophthalmic vision onto the back face of the eyeglass.

Description:

FIELD OF THE INVENTION

[0001] The invention relates to an eyeglass adapted for providing both an
ophthalmic vision and a supplementary vision to a wearer of this
eyeglass.

BACKGROUND OF THE INVENTION

[0002] Such eyeglasses are already known, for example from WO 2008/003903.

[0003] The ophthalmic vision is the usual or natural vision by the wearer
of actual objects existing in his environment. It may be improved by
using ametropia-correcting eyeglasses or solar eyeglasses, for example.
But such eyeglasses do not modify the information content of the image.

[0004] The supplementary vision is intended to provide the wearer with
supplementary information, or extra information. This supplementary
information may be data which are displayed for the wearer to see them.
For example, piloting data may be displayed on the visor of a pilot
helmet, so that these data appear superposed to the image of the
ophthalmic vision. Another example of supplementary vision is to supply
the wearer with modified images of parts of his environment. Such
modified images may be magnified images of infrared images converted into
visible light images.

[0005] Referring to FIG. 1, an eyeglass 10 which is adapted for providing
at least the ophthalmic vision and the supplementary vision to the wearer
may comprise: [0006] a front face FF and a back face BF, which are
intended to be oriented respectively away from and towards an eye 20 of
the wearer; [0007] a light-refracting transparent material 1, which is
comprised between the front face FF and the back face BF; and [0008] a
light-conducting element 2, which is located in the light-refracting
transparent material 1, and adapted to output a supplementary light SL
between the front face FF and the back face BF of the eyeglass 10,
through an exit face EF of this light-conducting element 2 and towards
the wearer's eye 20.

[0009] The exit face EF of the light-conducting element 2 is thus oriented
towards the eye 20, so that the supplementary light SL enters into the
eye 20 through the eye pupil P and reaches the retina R. Reference number
30 denotes a source unit which produces the supplementary light SL so
that this latter corresponds to a supplementary image after being output
through the exit face EF. Details of such source unit 30 are well-known
so that it is not necessary to repeat them here. This source unit 30
introduces the supplementary light SL into the light-conducting element 2
through an appropriate optical connexion therebetween.

[0010] The ophthalmic vision corresponds to the image formed by light OL
transmitted by the eyeglass 10 from its front face FF to its back face
BF, also entering into the eye 20 through the pupil P and reaching the
retina R. The image of the ophthalmic vision is called natural image
thereafter.

[0011] The supplementary vision corresponds to the supplementary image to
be viewed by the wearer, which is formed by the supplementary light SL.

[0012] Furthermore, the light-conducting element 2 is transparent for the
light OL of the ophthalmic vision. Thus, the eyeglass 10 is capable of
providing both the natural image and the supplementary image to the
wearer, simultaneously or even alternatively.

[0013] Because the front face FF and the back face BF have respective
curvatures, they each produce an optical power. Since the light OL which
is efficient for the ophthalmic vision intersects both the front face FF
and the back face BF of the eyeglass 10, the optical power of this
eyeglass for the ophthalmic vision is the algebraic sum of the respective
optical powers of the two faces. But the supplementary light SL is output
by the light-conducting element 2 between the two eyeglass faces FF and
BF, so that it intersects only the back face BF when propagating towards
the wearer's eye 20. So only the optical power of this back face BF is
efficient for the supplementary vision. Thus the eyeglass 10 produces
effective optical powers which are different for the ophthalmic vision
and the supplementary vision. As a consequence, the natural image and the
supplementary image do not appear sharp at the same time to the wearer.

[0014] One possibility for the two images to be sharp at the same time on
the wearer's retina R is to provide the source unit 30 with a focussing
unit. Such focussing unit can be adjusted so that the supplementary image
is formed on the retina R at the same time the eye 20 is focussed for
staring at the natural image. Then both images appear sharp, but such
focussing unit is expensive and needs to be operated by the wearer.

[0015] According to WO 2008/003903, another possibility is to limit the
curvature of the front face FF so as to maintain the optical power
produced by this face below an accommodation threshold of the eye 20.
Then, the light OL of the ophthalmic vision is not much altered by the
front face FF of the eyeglass 10, and the light beams of both the
ophthalmic vision and the supplementary vision are affected in a similar
extent by the eyeglass 10. But the accommodation threshold varies
depending on the wearer. In addition, the limited curvature of the front
face of the eyeglass generates optical distortions for oblique gaze
directions.

[0016] A third possibility is to design the back face BF of the eyeglass
10 for producing an appropriate optical power for the supplementary image
being focussed on the wearer's retina R. Then the front face FF can be
adjusted so as to focus the natural image on the retina R through the
back face BF. But according to this method, both faces BF and FF of the
eyeglass 10 have to be adjusted once the ametropia of the wearer is
known. Therefore, using semi-finished eyeglasses with one of the faces
thereof being final from the semi-finished eyeglass production is not
possible. In addition, the curvatures of both faces FF and BF may
generate important optical distortions for the natural image.

[0017] Then, a first object of the present invention is to provide an
eyeglass with both the ophthalmic and the supplementary vision, with the
natural image and the supplementary image being focussed sharply on the
wearer's retina during respective periods.

[0018] A second object of the invention is to provide such eyeglass which
does not generate significant distortions at least for the natural image.

[0019] A third object of the invention is to provide such eyeglass which
can be produced using the semi-finished eyeglass production stage.

SUMMARY OF THE INVENTION

[0020] To this purpose, the invention proposes an eyeglass adapted for
providing at least the ophthalmic vision and the supplementary vision to
the wearer with the features recited above, and which further comprises a
transparent active device. This device is located between the exit face
of the light-conducting element and a portion at least of the back face
of the eyeglass. It is also adapted for producing a variable optical
power depending on a control signal which is supplied to this transparent
active device. Then, first and second values for the variable optical
power are different from each other, and correspond respectively to a
first and a second state of the transparent active device.

[0021] First and second states of the transparent active device are
respectively dedicated to the supplementary vision and the ophthalmic
vision. Thus, the transparent active device in the first state is
effective for the supplementary light, and the first value of the
variable optical power is suitable for the supplementary image to appear
sharp to the wearer. Furthermore, the light-conducting element is
transparent for the light of the ophthalmic vision. Then, the transparent
active device is effective in the second state for the light of the
ophthalmic vision which is transmitted through the exit face of the
light-conducting element, and the second value of the variable optical
power is suitable for the natural image to appear sharp to the wearer in
turn.

[0022] Hence, the natural image and the supplementary image are focussed
on the wearer's retina during periods where the transparent active device
is in the second and the first state, respectively.

[0023] Because the appropriate optical power for the supplementary vision
is provided by the transparent active device, the front face and
optionally the back face of the eyeglass can be optimized for the
ophthalmic vision. Then, this or these face(s) can be designed so that
the natural image is devoid of any important optical distortions. In
addition, the front face and the back face of the eyeglass may be used
for providing the wearer with an appropriate ametropia correction, which
is effective for the ophthalmic vision. In such case, the transparent
active device cooperates with the back face of the eyeglass for
correcting the wearer's ametropia for the supplementary vision, depending
on the location of the supplementary image as output directly by the
light-conducting element.

[0024] In a preferred embodiment of the invention, the transparent active
device may be entirely embedded in a rear portion of the light-refracting
transparent material, which is located between the exit face of the
light-conducting element and the back face of said eyeglass.

[0025] In such case, because the supplementary image is focussed on the
wearer's retina independently of the front face of the eyeglass, this
eyeglass can be produced using the intermediate stage of semi-finished
eyeglass. Such semi-finished eyeglass may comprise a portion of the
light-refracting transparent material with a final front face, and with
the light-conducting element and the transparent active device both
embedded therein. Then, semi-finished eyeglasses may form a collection
with variable front face mean curvature values, also called base values.
This is especially cost-effective, because the semi-finished eyeglasses
can be mass-produced in large scale plants, and the back face of each
semi-finished eyeglass can be shaped according to a user's prescription
in laboratories out of the large scale plants. So the invention makes it
possible to produce finished eyeglasses with ophthalmic and supplementary
visions using the same production scheme as already implemented for usual
eyeglasses.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1 is a perspective view of an eyeglass known before the
present invention.

[0027] FIGS. 2a and 2b are respectively a perspective view and a sectional
view of an eyeglass according to the present invention.

[0028] FIGS. 3a and 3b are respectively a front view and a sectional view
of a transparent active device which may be used in an embodiment of the
present invention.

[0029] FIGS. 4 and 5 are respective sectional views of other transparent
active devices which may be used in alternative embodiments of the
present invention.

[0030] For sake of clarity, the elements represented in these figures are
not sized in relation with actual dimensions, nor with ratios of actual
dimensions. In addition, same reference signs indicated in different
figures denote similar elements or elements with similar functionalities.

DETAILED DESCRIPTION OF THE INVENTION

[0031] FIG. 1 which relates to prior art has already been described.

[0032] According to FIGS. 2a and 2b, an eyeglass 10 according to the
invention comprises the same elements as the eyeglass of FIG. 1, namely
the light-refracting transparent material 1 limited by the front face FF
and the back face BF of the eyeglass, and the light-conducting element 2
with its exit face EF for the supplementary light SL. The
light-conducting element 2 is preferably entirely embedded within the
light-refracting material 1, so that a rear portion 1r of the
light-refracting transparent material 1 is located between the exit face
EF of the light-conducting element 2 and the back face BF of the eyeglass
10. The light-refracting transparent material 1 extends continuously
between the light-conducting element 2 and the front face FF.

[0033] The light-refracting transparent material 1 may be any material
commonly used in ophthalmics.

[0034] The light-conducting element 2 may be of any design already known
and described in documents focussed on such element.

[0035] The source unit 30 does not pertain to the eyeglass 10 which is the
subject-matter of the present invention. It produces the supplementary
light SL and inputs it into the light-conducting element 2.

[0036] The eyeglass 10 of the invention further comprises a transparent
active device 3, which is located between the exit face EF of the
light-conducting element 2 and the back face BF of the eyeglass. When the
rear portion 1r exists for the light-refracting transparent material 1,
the transparent active device 3 is preferably contained in this rear
portion. Preferably but not necessarily, it is entirely embedded within
the rear portion 1r.

[0037] The transparent active device 3 extends parallel to the back face
BF over an area which is at least equal to the projected area of the exit
face EF of the light-conducting element 2. Preferably, the respective
areas of the transparent active device 3 and the exit face EF match each
other when projected onto the back face BF of the eyeglass 10 along light
rays of the ophthalmic vision.

[0038] Mainly, the transparent active device 3 operates like a
controllable lens, which produces an optical power that can vary between
two values different from each other. One of these values for the
variable optical power of the transparent active device 3 may be zero.

[0039] In simple embodiments of the invention, the transparent active
device 3 may be liquid crystal-based.

[0040] In first and second embodiments, the transparent active device may
comprise a portion of liquid crystal which is contained between two
surfaces, with at least one of these surfaces being provided with a
Fresnel pattern. It further comprises two electrodes which are arranged
for modifying an orientation of the liquid crystal upon a variation of an
electrical voltage V that is applied to said electrodes. FIGS. 3a and 3b
illustrate such first embodiment with a Fresnel pattern provided on only
one of the surfaces limiting the liquid crystal portion. Such device
structure is described in particular in document WO 2009/045533. FIG. 4
illustrates a second embodiment with two Fresnel patterns which are
provided respectively on the two surfaces which limit the liquid crystal
portion, as described in US 2007/216851. In these figures, the following
reference numbers denote the elements now listed: [0041] 30: the
portion of liquid crystal, [0042] 3ff, 3bf: front surface and back
surface limiting the liquid crystal portion 30, [0043] 31a, 31b: Fresnel
patterns, [0044] 32, 33: electrodes, [0045] 34: an electric power supply
generating the variable voltage V, and [0046] 38, 39: plates containing
the portion of liquid crystal 30 therebetween.

[0047] Thanks to the plates 38 and 39, the transparent active device 3 can
be manufactured separately at first, and embedded afterwards together
with the light-conducting element 2 within the light-refracting material
1, during the moulding of the eyeglass 10.

[0048] The actual operation of these devices is well-known, so that is not
necessary to repeat it again in this description. In particular, at last
one of the surfaces 3ff and 3bf of the each device 3 may be structured so
as to orientate the liquid crystal portion 30 when the electrical voltage
V is zero or below a switching threshold.

[0049] In a third embodiment illustrated by FIG. 5, the transparent active
device 3 may comprise a set of cells C which are juxtaposed parallel to
the exit face EF of the light-conducting element 2 in the eyeglass 10.
The cells C are separated from each other by a network of walls 40 each
extending perpendicular to the exit face EF. Each cell C contains a
portion 35 of liquid crystal. The transparent active device 3 further
comprises at least the electrodes 36 and 37. The electrodes 36 and 37 are
arranged for modifying an orientation of the liquid crystal portion 35 in
each cell C when an appropriate variation of at least one electrical
voltage is applied to these electrodes. The respective liquid crystal
portions 35 of the cells C are suitable for the transparent active device
3 to produce the variable optical power. Actually, such transparent
active device is a spatial light-phase modulator designed for operating
as a variable lens. Depending on the detailed operation of the device 3,
the electrodes 36 and 37 may be replaced each with multiple electrodes so
that the electrical voltage applied may vary over the extent of the
device.

[0050] The total optical power of the eyeglass 10 for the supplementary
light SL is the sum of the optical power of the transparent active device
3 and that of the back face BF. In parallel, the total optical power for
the ophthalmic light OL is the sum of the optical power of the
transparent active device 3 and those of both the front face FF and the
back face BF.

[0051] Generally, the transparent active device 3 switches between two
states: a first one intended to be selected when the user gazes at the
supplementary image formed by the supplementary light SL, and a second
one intended to be selected when the user gazes at the natural image
formed by the ophthalmic light OL. For the implementations of FIGS. 3a,
3b and 4, each state corresponds to a different orientation of the liquid
crystal of the portion 30. For the implementation of FIG. 5, each one the
two states is defined by a set of respective orientations of all the
crystal portions 35 which are produced simultaneously. In every case, the
optical power of the transparent active device 3 varies from a first
value in the first state to a second value in the second state.

[0052] Preferably, the difference of the first value minus the second
value for the variable optical power of the transparent active device 3
may be greater than the optical power of the front face FF of the
eyeglass 10. This ensures that the user can view clearly the
supplementary image even if this image is located quite close to his eye,
and even if the user is long-sighted, also called hypermetropic. For
calculating and comparing the optical power values, signed values are
considered in a usual way.

[0053] Also in preferred embodiments of the invention, the second state
may be a default state of the transparent active device 3. Such default
state is effective when the power supply of the transparent active device
3 is off or exhibits an operation failure, for example. This complies
with safety reasons, for example when the user is driving, and makes
energy savings when the supplementary vision is to be used during limited
durations.

[0054] One skilled in ophthalmics will understand that the invention is
compatible with any ametropia the user may have, in particular myopia and
hypermetropia. Indeed, such ametropia may be corrected by shaping
appropriately the front face FF and/or the back face BF of the eyeglass
10 for the ophthalmic vision, whereas the transparent active device 3 is
used for correcting the ametropia for the supplementary vision, further
to the optical power of the eyeglass back face BF.

[0055] Finally, it is possible that the transparent active device 3 be
adjacent to the back face BF of the eyeglass 10. Then it forms itself a
portion of this back face BF at least behind the exit face EF of the
light-conducting element 2. The transparent active device 3 may also be
glued on the back face BF of the eyeglass 10. In such case, it may be
resilient so as to conform with the initial shape of the back face BF.
When the exit face EF of the light-conducting element 2 forms directly a
portion of the initial back face of the eyeglass 10, then the transparent
active device 3 may be glued directly onto the light-conducting element
2, over the exit face EF.